As Presented by Lori Watt & Matt Medwick

As Presented by Lori Watt & Matt Medwick

Jumping Dimes

As presented by Lori Watt & Matt Medwick

Purpose

To show the force that can be exerted on an object by reducing the air pressure on one side of it.

Materials

  • A bunch of dimes, enough for several groups of people
  • Plates of substantial weight (not paper), one for each group

Safety Considerations

In general this is a very safe experiment for high school students, but just to be safe: Make sure no one puts the coins in their mouth and if a plate breaks accidentally be sure to sweep it up as soon as possible. Also, advise students to wash hands after handling coins they are dirty.

Connections to the Curriculum

This discrepant event is intended for a grade ten audience where recall/comprehension of a concept learned previously will be needed for completion of a SLO in the grade ten curriculum. The students’ entry-level knowledge in this case came from grade five specific learning outcomes where the study of weather was first introduced to them.

SLO: 5-4-03 GLO: D3

Describe properties of air. Include: exerts pressure, moves from areas of high pressure to areas of low pressure.

Between the grade five curriculum, real life experiences related to severe weather and exposure to the media, students in grade ten have the knowledge necessary to formulate ideas pertaining to this discrepant event. As stated above this discrepant event addresses a concept necessary to achieve the following specific learning outcome from the grade ten science curriculum in a following lesson.

SLO: S2-4-04 GLO: A2, D5, E1, E4

Explain the formation and dynamics of severe weather phenomena.

In order to address such a broad topic, it is important to revisit previous learning to gain understanding for new higher level learning. It is important to have in place some solid basis upon which to address the dynamics of severe weather as outlined in the learning outcome.

Teaching Sequence

Before Students Arrive

  1. Collect materials necessary to carry out the demonstration.
  2. Set up the classroom so that there are several different groups of students sitting around tables.
  3. Distribute one plate to each table and place in the center, as well as enough dimes for each student at all of the tables.

After Students Arrive and Settle

  1. Ask students to try to figure out how to place their dime onto the groups’ plate without physically touching either of the materials or anything around them. (Make sure if someone has seen this before they know not to tell the others how this can be done)
  2. Let the students’ contemplate and try out their ideas for a short while with their group. (The normal response to this task would be something along the lines of “This is impossible”)
  3. Ask the students if they have any ideas how to complete the task. What and why?
  4. Continue on by telling the students that this lesson is on the effects of air pressure.
  5. Now change your original question to “now using the concept of air pressure can you predict a way to get the dime onto the plate?”
  6. Again let the students think about the task for a short while with the new concept in mind.
  7. Ask once again if they have any ideas how to accomplish the task at hand. (If they do, great, get them to show/discuss with the class while the class observes and if they still don’t have much idea then proceed to the next step that is the actual event demonstrated by a teacher.)
  8. Place the plate on the table with the edge of the plate about 12cm from the edge of the table. Put the dime about 4cm from the table edge; position your mouth to blow OVER the dime and towards the plate. Do not blow directly onto the dime. Use a quick hard puff and the dime should ‘jump’ to the plate.
  9. Get the students to try this themselves a few times.
  10. Allow students some time in their groups to discuss how and why this works.
  11. Ask for some explanations that were being discussed.
  12. Give a further explanation if needed on this basic concept.
  13. By blowing directly over the dime this will increase the air speed over the top of the dime and thus decrease the air pressure in that area which results in the dime being pushed up into the stream of air by the higher pressure coming from underneath the coin. (see theoretical background for further details)

Extensions of the Demonstration

  1. What if students try to get different objects or coins to jump? What will happen if they are of different shape, size or weight?
  2. What will happen if you blow at a different angle to the object? Or what if you prop the object up on something?
  3. What happens if you use a different amount of force in your breath to either increase or decrease the speed of air crossing over the object?
  4. What if you made this activity into a contest for fun to see which team or which student could make their coin jump the highest/furthest, and how they did it?
  5. From this demonstration connections could also be made to real life; for example, pressure systems in weather (which would be a good transition to the big picture learning outcome S2-4-04 which will be discussed in later lessons), this event could also be connected to the concept of lift which could then be connected to flight, how frisbees work, or the basics of airplane flight etc.
Theoretical Background

The atoms and molecules that make up the various layers in the atmosphere are always moving in random directions. Despite their small size, air exerts a pressure on everything within it and everything around it. Since molecules move in all directions, they can even exert air pressure upwards as they hit a surface from underneath an object. The change in pressure measured across a given distance is called a pressure gradient. This pressure gradient results in a net force that is directed from areas of high to low pressure. Lift is also a term used for the force that will push an object up against the natural force of gravity as demonstrated in the discrepant event. This enables an object to climb into the air and remain aloft. The force of horizontally moving air (our breath in this demonstration) is being used to overcome the downward pull of gravity. As the speed of air over the object is increased, pressure is decreased in this area, which equals a force pushing up on the object to produce lift. This whole concept of moving air has been harnessed to be useful for thousands of years for instance with the use of sailboats, windmills and airplanes. However it can also be destructive which happens in events such as hurricanes and tornadoes.

How Does This Event Create Disequilibrium?

We believe that this experiment is an excellent discrepant event for a few reasons. In the Manitoba curriculum we found that the grade 5 science class includes lessons on weather so the grade ten students should have a basic understanding of various weather phenomena. In addition, we also found that in the grade 6 curriculum there are lessons on flight, which in some aspects will help to make additional connections between science and real life. So, although the students should possess all the knowledge necessary to solve this riddle of the jumping dime right from the beginning of the lesson they will have to think critically to come to the right correct prediction. The discrepancy first comes into play when the students are forced to guess how to get the coin onto the plate without physically touching anything. In most cases they will automatically think this is impossible which creates disequilibrium. After giving them a clue about air pressure the students will still have to think critically to be able to put the concept to use. At this point some students may figure it out and others may not. When the actual event is demonstrated, we still think it involves discrepancy because although the students may now know that it happens because of air pressure they will still have to explain how you can make a coin ‘jump’. We believe that although this is a simple demonstration, it involves a lot of thinking on the students’ part. We also believe that this is an excellent experiment for a science class because it can be adapted to suit the needs of various grade levels depending on how in depth you would like to go with it. As well, there are applications of this phenomenon to the world surrounding us, which will help us as teachers answer the typical “why do we need to learn this stuff?”

References

Brent, B.A. (2002). Science Demonstrations Presented at NSTA. Retrieved September 26, 2007, from

National Weather Service. (2007). Air Pressure. Retrieved September 26, 2007, from

Encyclopedia of the Atmospheric Environment. (n.d.) Pressure. Retrieved September 26, 2007, from

The National Business Aviation Association. (1997). Lift. Retrieved September 26, 2007, from

Manitoba Education and Training. (2000). Grades 5 to 8 Science – A foundation for implementation. Winnipeg, Manitoba.

Manitoba Education and Training. (2003). Senior 2 Science- A foundation for implementation. Winnipeg, Manitoba.

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